source-twilio: improve MessageMedia incremental sync speed

`MessageMedia` was previously checking every message between the
config's start date and the present for new media, then filtering out
any media created before the cursor value. That made incremental syncs
take an extremely long time without any apparent progress; the stream
could be searching through the past few years of messages when it
usually only needs to search through the past few minutes.

This change makes the `MessageMedia` stream only check messages created
since the most recent cursor value, falling back to the config's start
date if no cursor value is present. This significantly speeds up the
connector during incremental syncs.

This change also increases the date window size used when fetching a
message's media from 1 year to 100 years. This reduces the number of API
requests needed when backfilling media records over a year old; instead
of requesting a single year of media at a time, the connector
essentially requests all of a message's media in one request.

It would make more sense to not use a sliding date window strategy for
fetching a single message's media, but rewriting the `MessageMedia`
stream in a backwards compatible way is a large effort I'd like to
avoid, especially when small, targeted changes address the current issue.

source-twilio/source_twilio/streams.py

@@ -557,17 +557,23 @@ class Messages(IncrementalTwilioStream, TwilioNestedStream):
 class MessageMedia(IncrementalTwilioStream, TwilioNestedStream):
     """https://www.twilio.com/docs/sms/api/media-resource#read-multiple-media-resources"""
 
-    parent_stream = Messages
+    parent_stream: type[Messages] = Messages
     data_field = "media_list"
     subresource_uri_key = "media"
     media_exist_validation = {"num_media": "0"}
     lower_boundary_filter_field = "DateCreated>"
     upper_boundary_filter_field = "DateCreated<"
-    cursor_field = "date_created"
+    cursor_field: str = "date_created"
+    # Per the Twilio docs on updating Messages, media can't be added to/updated within a message after
+    # the message is created, so it doesn't make sense to use small date windows to check for a message's media.
+    # Making slice_step_default (i.e. the window size) really large reduces the number of requests we need
+    # to get all of a message's media without significantly rewriting how this stream works.
+    slice_step_default = pendulum.duration(years=100)
 
     @cached_property
     def parent_stream_instance(self):
-        return self.parent_stream(authenticator=self.authenticator, start_date=self._start_date, lookback_window=self._lookback_window)
+        most_recent_cursor = self.state.get(self.cursor_field, self._start_date)
+        return self.parent_stream(authenticator=self.authenticator, start_date=most_recent_cursor, lookback_window=self._lookback_window)
 
 
 class UsageNestedStream(TwilioNestedStream):